1. Field of the Invention
The present invention relates generally to a method and apparatus for coordinating the operation of multiple remotely operated or autonomous marine vessels engaged in marine seismic data acquisition comprising a vessel management system and in particular to a real-time feed back and positioning method and apparatus that will to provide a recommendation for optimal midpoint coverage.
2. Description of the Related Art
The prior art discloses a wide variety of marine seismic systems with one or more streamers and/or one or more seismic sources, some of which include a main or host vessel and other unmanned remote control vessels, or apparatuses such as floats, paravanes, or buoyant members which are connected to the host vessel by lines, streamer cables or tethers. Considerable power is required for a host vessel to tow such existing seismic streamer systems and cables interconnecting sensing devices with a tow vessel. A typical host vessel is able to tow a plurality of associated vessels or apparatuses and can carry a plurality of undeployed seismic streamers and associated apparatuses.
With known cable tow systems, the location and spacing of system components is illustrated by the type, size, and length of cables used and by the characteristics of tow vessels and other devices of the systems. Changing the configuration of an array of prior art components, e.g., streamers can be a complex, time-consuming operation.
U.S. Pat. No. 5,724,241, entitled xe2x80x9cDistributed Seismic Data-Gathering System,xe2x80x9d by Wood, et al., describes a distributed seismic data acquisition system of a plurality of Autonomous Data Acquisition Modules (ADAMs) to each of which are interconnected a subplurality of data-collection channels. Each data collection channel is composed of an array of seismic sensors for continuously measuring seismic signals. The ADAMs includes a GPS satellite receiver for providing geographic coordinates and a system clock. Measured seismic signals are quantized and continuously downloaded to respective interconnected ADAMs from the data-collection channels. The system includes both field-testing capability as well as means for transmitting the results of self-tests.
During a typical marine seismic survey a seismic vessel traverses programmed tracks towing arrays of seismic sources and seismic streamer cables. A seismic streamer cable normally contains a plurality of hydrophones that convert seismic pressure waves, initiated by the sources and reflected from the subsurface geological formations, into electrical signals, which are recorded on a marine seismic data acquisition system located on the vessel. Due to the increasing use of marine three-dimensional (3-D) seismic data, multi-cable marine surveys are now commonplace. During a typical marine 3-D seismic survey, a vessel may tow as many as ten or more streamer cables, with cables ranging in length from three to eight or more kilometers. As reported by Gadallah in xe2x80x9cReservoir Seismologyxe2x80x9d 1994, pp. 209-237, the goal of a normal marine 3-D seismic survey is to use these arrays of seismic sources and streamer cables to record a highly sampled grid of xe2x80x9cbinsxe2x80x9d of subsurface seismic coverage.
A natural consequence of towing such streamer cable configurations in a marine environment is that currents, wind, and wave action will deflect the streamer cables from their intended paths. Streamer cable drift presents a continuing problem for marine seismic surveys. See, for example, U.S. Pat. No. 5,532,975. The ability to control the position and shape of the streamer cables is desirable for preventing the entanglement of the streamer cables and for avoiding collisions with offshore hazards such as marine drilling rigs and platforms. It is also desirable to have the ability to control the position and shape of the streamer cables during marine 3-D seismic surveys because the 3-D seismic binning process acquires subsurface seismic coverage by combining seismic data from different lines. The need for ability to control the position and shape of the streamer cables is taught by Franklyn K. Levin in xe2x80x9cShort Note: The Effect of Binning on Data from a Feathered Streamer,xe2x80x9d Geophysics, Vol. 49, No. 8, pp. 1386-138,7.
Streamer positioning devices are well known in the art. Apparatuses, such as those disclosed in U.S. Pat. Nos. 5,532,975; 4,729,333; and 4,463,701, have been devised for attachment to the front end of streamer cables for the purpose of maintaining them at a lateral offset to the pathway of the towing vessel. Steerable tail buoys, as described in U.S. Pat. No. 4,890,568, have also been designed for controlling the position of the tail end of seismic streamer cables. The prior art also discloses streamer positioning devices that may be attached externally to the streamer cables. For example, devices to control the lateral positioning of streamer cables by using the camber adjustable hydrofoils or angle wings are disclosed in (U.S. Pat. Nos. 4,033,278 and 5,443,027. U.S. Pat. No. 3,931,608 describes an apparatus, typically known as a xe2x80x9cbirdxe2x80x9d, to control the vertical positioning of streamer cables with diving planes and a present depth control means.
The use of streamer positioning devices comes at the price of introducing increased noise onto the seismic streamer and hence into the hydrophones. The areas of greatest noise are from those hydrophones adjacent externally attached streamer-positioning devices, such as depth controlling birds. This problem has been described by Schoenberger and Misfud, xe2x80x9cHydrophone Streamer Noise,xe2x80x9d GEOPHYSICS, Vol. 39, No. 6, pp. 782-784. It is well known in the art that noise limits the resolution of a seismic survey. Consequently, a maximum allowable hydrophone noise level is typically established for each marine seismic surveying project. When this noise level is exceeded, seismic acquisition is usually suspended, resulting in lost time and additional cost. Data acquired under such conditions may need to be reacquired.
Location sensing devices and methods for determining the positions of the seismic sources and seismic streamer cables are also well known in the art. For example, both a Global Positioning System, as described in U.S. Pat. No. 4,809,005, and a network of acoustic elements, as described in U.S. Pat. No. 4,912,682 may be deployed on the vessel, streamer cables, and tail buoy. These devices and methods may then be used to determine the real time positioning of the seismic sources and seismic streamer cables by computing a network solution to a Kalman filter, as disclosed by U.S. Pat. No. 5,353,223.
As known to those familiar with the art of marine seismic surveying, during a typical seismic survey a human operator monitors the survey""s operational conditions, such as the extent of the subsurface seismic coverage, the adequacy of the separations between streamer cables, and the proximity of the streamer cables to obstructive hazards. When these conditions indicate the need to reposition the streamer cables, the operator may manually issue commands to the various individual streamer positioning devices in order to adjust the position and shape of the streamer cable, or order the helmsman or vessel remote control to redirect the vessel, or suspend data acquisition.
A typical three-dimensional marine geophysical survey is performed by transiting a pre-defined grid of parallel lines in order to cover a desired survey area at a required minimum multiplicity for common midpoint coverage. During each pass over the grid a spread of seismic sources and receivers is used to produce the desired subsurface common midpoint coverage. Because the seismic spread is perturbed due to errors in the towing vessel""s motion, tidal streams, ocean current, river estuaries, etc. sub-optimal midpoint coverage is obtained. To mitigate the loss of coverage an operator will attempt to maneuver the towing vessels to his or her interpretation of the best geometry. Such manual maneuvering is by nature a labor-intensive process and highly subject to operator bias, error and as such is prone to failure. To recover data caused by this lack of coverage, extra passes over the grid must be performed before the necessary common midpoint coverage can be achieved. These extra passes can significantly increase the survey costs. Thus, there is a need for a system that will, by maneuvering the vessels towing the seismic streamers and sources, optimize the common midpoint coverage obtained during acquisition, minimize the number of survey lines, the duration of the survey and thus the acquisition and post-acquisition processing costs.
While the prior art discloses a series of discrete devices for locating and controlling the positions of streamer cables, it does not teach or identify any single system which coordinates the movement of a plurality of remote vessels and attached seismic, position and environmental sensors to calculate optimal midpoint coverage vessel/sensor paths to maximize coverage of the plurality of remote vessels and the attached seismic sensors.
Thus there is a need for a single remote vessel management system which coordinates the movement of a plurality of remote vessels and attached seismic, position and environmental sensors and calculates optimal midpoint coverage for the vessel and source/sensor paths in order to maximize coverage and reduce non-coverage by the plurality of remote vessels and their attached seismic assets.
When multiple ships, whether manned or not, are used to acquire seismic data, they must be carefully positioned to maintain spatial configuration of the towed assets through a survey and also maintain the safety of the trailing assets, the vessel and crew. In the past, this has been accomplished by careful piloting by the ship""s crew augmented by radio voice communication. As the required precision has increased and new automatic positioning devices have become available, multiple ships have relied on auto helm systems and information sharing between ships. There has been a need for a system to autonomously coordinate the movement of multiple ships participating in a seismic survey to maximize safety for the vessels, seismic assets and crew while also minimizing deviations from desired spatial configuration of the assets.
The present invention provides a system that, by maneuvering vessels towing seismic streamers and sources, optimizes the common midpoint coverage obtained during seismic data acquisition, minimizes the number of survey lines, the duration of the survey and the acquisition and post-acquisition processing costs. The present invention provides a system that coordinates the movement of a plurality of remote vessels and attached seismic, position and environmental sensors to obtain optimal midpoint coverage vessel/sensor paths to maximize coverage of the plurality, of remote vessels and the attached seismic sensors within the constraints of safety for personnel and equipment.
In one aspect of the present invention, a method and system are provided for coordinating the operation of one or more marine vessels engaged in seismic data acquisition comprising at least one vessel for performing one or more of deploying a source of acoustic energy for generating acoustic waves, deploying a receiver for receiving seismic data, and a processor for monitoring a parameter of interest of the received seismic data and generating control commands for controlling the at least one vessel in response thereto, the vessel further comprising a position sensor for determining a position of at least one vessel, the source of acoustic energy, the seismic receiver, and a vessel maneuvering system comprising a receiver for receipt of vessel control commands, a processor interpreting vessel control commands, and an output for executing vessel control commands. An environmental sensor is provided for monitoring and transmitting environmental data to the processor.
The processor receives position, environmental and operation data and sends a vessel control command to the vessel maneuvering system. Vessel maneuvering includes changes in heading, speed or depth of operation. The environmental data comprises at least one of: wind speed, wind direction, wave height, wave direction, wave period, tidal stream, ocean current, or water depth. A coverage optimization system wherein the coverage optimization system receives seismic coverage information, and sends optimum seismic source and seismic receiver positions to the vehicle management system. The VMS sends commands to the steering system. A binning system provides seismic coverage data to the coverage optimization system. The coverage optimization system receives operator data, position data and environmental data. The position sensor monitors seismic source position, seismic receiver position, vessel position, vessel ground speed, water speed, vessel track, and vessel heading. An operator console for operator data input wherein the operator data comprises prospect coverage area definition, required midpoint coverage, operational constraints, vessel performance data, or operator control.
In another aspect of the invention a method and system are provided wherein the binning system provides a current seismic midpoint coverage assessment to the coverage optimization system. The vessel control command comprises optimum locations for at least one of the seismic source, the receiver, or the vessel. The coverage optimization system generates a pre-plan and line selection based upon the available source and receiver assets, environmental data, past performance and operational constraints. The coverage optimization system generates real-time optimum source and receiver locations using computed source, receiver and towing vessel coordinates, in-water asset dynamics, past midpoint coverage, midpoint coverage required, operational constraints and environmental data. The COS provides optimum locations, and the VMS produces steering commands based on tow vehicle limitations, hazards, etc. In another aspect of the invention a method and system are provided wherein the coverage optimization system generates a pre-plan and line selection based upon the available source and receiver assets, environmental data, past performance and operational constraints.